A conventional tubular strainmeter is disclosed in, for example, the patent document 1 cited below. The conventional tubular strainmeter is laid deeply in the ground of a hazardous area, as shown in FIG. 11, to detect and measure strains developed in tubes by means of internal strain gauges installed in the tubes, and to confirm the position of a landslide and to assess the landslide.
The conventional tubular strainmeter is installed as follows. First, an installation hole is pre-bored for the tubular strainmeter with a boring machine to a depth in the range from 20 to 30 m. Next, a strain gauge 5 is stuck on the outer peripheral surface of each steel tube (1a, 1b, 1c, . . . ). Each gauge is covered with a protective material. These steel tubes are connected together by fitting one end of a tube into another end of another tube using a joint tube 2 and fastening the joint tube 2 with a rivet 3, thereby forming a measuring tube 1, which is then inserted into the installation hole. Finally, cement milk is poured into the installation hole to fill the space in the hole and firmly fix the tube in the ground to improve the detection accuracy of the tubular strainmeter.
Patent document 1: Japanese Utility Model Registration No. 2514095.